1. Field of the Invention
The present invention relates to the field of downhole well tools. More specifically, the invention relates to a downhole tool that provides a selectively variable fluid flow area between the well annulus and the interior flow bore of a well tube.
2. Description of Related Art
The economic climate of the petroleum industry drives producers to continually improve the efficiency of their recovery systems. Production sources are increasingly more difficult find and exploit. Among the many newly developed production technologies is directed drilling. Deviated wells are drilled to follow the layering plane of a production formation thereby providing extended production face within the production zone. In other cases, a wellbore may pass through several hydrocarbon bearing zones.
One manner of increasing the production of such wells is to perforate the well production casing or tubing in a number of different locations, either in the same hydrocarbon bearing zone or in different hydrocarbon bearing ones, and thereby increase the flow of hydrocarbons into the sell. However, this manner of production enhancement also raises reservoir management concerns and the need to control the production flow rate at each of the production zones. For example, in a well producing from a number of separate zones, or lateral branches in a multilateral well, in which one zone has a higher pressure than another zone, the higher pressure zone may produce into the lower pressure zone rather than to the surface. Similarly, in a horizontal well that extends through a single zone, perforations near the xe2x80x9cheelxe2x80x9d of the well (nearer the surface) may begin to produce water before those perforations near the xe2x80x9ctoexe2x80x9d of the well. The production of water near the heel reduces the overall production from the well. Likewise, gas coning may reduce the overall production from the well.
A manner of alleviating such problems may be to insert a production tubing into the well, isolate each of the perforations or lateral branches with packers and control the flow of fluids into or through the tubing. However, typical flow control systems provide for either on or off flow control with no provision for throttling of the flow. To fully control the reservoir and flow as needed to alleviate the above-described problems, the flow must be throttled.
A number of devices have been developed or suggested to provide this throttling although each has certain drawbacks. Note that throttling may also be desired in wells having a single perforated production zone. Specifically, such prior art devices are typically either wireline retrievable valves, such as those that are set within the side pocket of a mandrel or tubing retrievable valves that are affixed to the tubing.
An object of the present invention is a downhole valve for well flow regulation that incorporates a sliding sleeve to alter the fluid flow area between the well annulus and well tube flow bore. The tubular valve housing is ported with fluid flow openings in cooperative alignment with fluid flow ports through the sliding sleeve. When the sleeve ports are aligned with the housing ports, fluid flow is accommodated between the well annulus and the tube flow bore. When the sleeve ports are axially offset from the housing ports, fluid flow between the well annulus and the tube flow bore is obstructed. Sleeve port alignment is in graduated increments between a fully open valve and a fully closed valve.
Each increment of sleeve displacement is driven by a predetermined volume of hydraulic fluid released from a novel stepping valve. In one directional sequence, a distinctive fluid pressure also is required to step the sleeve from the prior increment to the next. Accordingly, greater fluid pressure is required to increase the valve flow area from one area increment to the next. Moreover, the pressure required for each shift of the sleeve is distinctive to the flow area increment that the sleeve is advancing toward (or from).
At each incremental location of the sleeve, the sleeve position is secured by a respective detent channel that accommodates a resiliently expanding snap ring. Each ring detent is flanked by a channel wall set at a predetermined acute angle. Steepness of the channel wall dictates the pressure required to radially constrict the resiliently biased snap ring. Provision of a distinctive channel wall angle respective to each valve flow area setting of the sleeve translates to a distinctive hydraulic pressure from the stepping valve essential to shift the sleeve from a particular setting.